Techniques for compacting aluminum powder mixtures



May 10, 1966 A. BARTOSZAK TECHNIQUES FOR COMPACTING ALUMINUM POWDERMIXTURES Filed Aug. 4, 1964 M/n/vs- 0F ALUMINUM P014051 Co ce HAM:

(l- 5 Z By L/E/GHT) COMPACT/OI) Or Gmselv Com /yer (HIGH 0. 10M DMs/rr)3900a cr INVENTOR. ANTHONY BAPTOSZAK 'occurs on ejection from the die.

United States Patent 3,250,838 TECHNIQUES FOR COMPACTING ALUMINUM POWDERMIXTURES Anthony Bartoszak, Brooklyn, N.Y., assignor to Alloys Research& Manufacturing Corporation, Woodside, N.Y., a corporation of DelawareFiled Aug. 4, 1964, Ser. No. 388,981 11 Claims. (Cl. 264-111) Thisapplication is a continuation-in-part of application Serial No. 202,582,filed June 14, 1962, and now abandoned.

This invention relates generally to powder metallurgical techniques forfabricating solid and porous bodies by pressing and sintering aluminumand copper powder mixtures, and more particularly to techniques forimproving the pressing characteristics of such mixtures and facilitat-'ing the sintering of compacts formed thereby.

In the co-pending application of Samuel Storchheim, filed November 7,1961, Serial No. 150,826, there is disclosed a. technique for formingporous and high-density bodies, such as porous bearings and structuralparts, by compacting a powder mixture of aluminum and copper particles,the copper content being in the range of 1% to 5% by weight. The greencompact is removed from the die and then sintered to form the desiredproduct.

Aluminum powders are notoriously difiicult to compact, for they exhibitsevere galling and seizing tendencies when pressed in steel dies. Thischaracteristic is particularly troublesome when the powders containsubstantial percentages of fines (-325 mesh fraction); As a result, ithas heretofore been the practice to mix in die lubricants such asstearates with the powders. However, it has been found that theexcessive use of lubricants results in dis coloration, oxidation, lowerstrengths, and lack of ductility in the sintered compacts. In fact, whensuch compacts are subjected to high pressures to obtain betterdensification in the green compact, catastrophic cracking often vTherefore, it has been felt that die wall lubrication rather than powderlubrication is the only possible solution to the compaction problemsencountered.

This solution, however, is not commercially feasible when one considersthat a commercially competitive powder metallurgy process requires thepressing of 30 or more pieces per minute. If die wall lubrication isused, it is found that commercial press manufacturers have difficulty indesigning high-speed presses in which the die walls are cleaned and thenrelubricated between pressings. Other problems encountered in sinteredparts are aggra- Summary of compaction data obtained for Patented May10, 1966 account, is that finely divided powders involve the hazard ofexplosions or fires which may occur in normal production handlingoperations.

The object of this invention is to overcome the abovenoted problemsheretofore encountered in pressing powder mixtures including aluminumfines, and in sintering the green compacts.

I have discovered that the use of flake powders as alloy additions(e.g., copper) to other metal powders such as aluminum, results inimproved pressing and sintering characteristics not heretoforeattainable with spherical and/ or atomized aluminum powders regardlessof mesh size or fractions used. The following basic advantages are foundtoexist:

(1) The use of flakes results in uniformly coating metal particulates ofthe major metal or alloy with a metal that is soft and malleable, whichin turn provides better pressing characteristics than attainable withother powder additions.

(2) The use of flake material results in uniform distribution of thealloying element throughout the green compact, which leads to maximumuniformity of diffusion in sintering and dimensional control.

(3) Flake coating has been found to be applicable to all shapes andsizes of powders or particulates, and has been used on needles as wellas atomized powders.

(4) Flake coating allows one to press parts with higher L/D to ratiosthan normally feasible. It is believed that this is partially due to thefact that the flake material has lubricating properties.

(5) The powder mixtures can .be vibrated with no apparent settlingoccurring, provided that a lubricant such as Sterotex is added to themixture. Without the Sterotex addition, the powders cannot be blended.

(6) It is now possible with this development to chop up scrap metal,coat it, and then press and sinter.

For a better understanding of the invention as well as other objects andfeatures thereof, reference is had to the following detailed descriptionto be read in conjunction with the accompanying drawing, wherein thesingle figure is a flow chart illustrative of the steps involved in thetechniques.

I have'discovered that aluminum powders containing 40 w/o or more of the325 mesh fraction can be safely handled and efliciently pressed at arapid rate by adding small percentages of a flake powder such as copperto the aluminum, as described in the following examples.

TABLE I powders containing 40 w/o or more fines Mixture compositionTheoretical density, qm .lcc.

Weight of compact, qms.

Height of compact,

Compacted percent theoretical density 1 Composition A-96 w/o aluminumpowder, 100 w/o through 40 mesh and 40 w/o through 325 mesh. Averageparticle diameter, 26 microns. Average apparent density, 1.0 gmsJcc.

Approximate specific gravity, 2.72. wlo+200 mesh. Apparent density,4.0-5.0 gm./cc.

1 w/o copper flake #44. 1 w/o copper powder, -100 2 w/o Sterotex.

2 Composition B46 w/o aluminum powder, 72.2-81.4 wlo+200 mesh, 18.2-24.2w/o 200 +325 mesh, 0.25-1.85 w/o -325 mesh. flake #44. 2 w/o Sterotex.

50 w/o aluminum powder, -325 mesh.- 2 W/o copper 3 Composition C-96 w/oaluminum powder, 100 w/o through 40 mesh and 40 w/o through 325 mesh.Average particle diameter, 26 microns.

Average apparent density, 1.0 grn./cc.

Appropriate specific gravity, 2.72. 2 w/o copper flake #44. 2 w/oStcrotex.

4 Maxnnum density obtained in a single pressing. Further compactionwould result in lamination of the compact upon ejection from the die.

In Step A, the powder mixture compositions indicated in Table I weremixed in a blender for approximately one hour prior to compaction in acommercial automatic double-acting mechanical press at a rate of over 30compacts per minute. The data for compactibility recorded in the tablewere obtained on typical random samples. No galling or seizing ofpowders on the die walls or punches occurred in any case.

In Step B, Composition A was pressed using a 0.750" diameter steel diewith a core rod having a 0.4985" diameter, thereby producing asleeve-type cylinder. Composition B was pressed into solid cylindersusing 0.750" diameter solid punches and no core rod.

In Step C, samples of Composition A were sintered for /2 hour in a dryhydrogen atmosphere at temperatures Ordinarily, green densities above80% of theoretical are not attainable when using mixture of similarlyshaped powders. This limitation occurs because of die-sticking and/ orseizure and die-scoring problems. In the present discovery, the flakeparticles, not only coat the aluminum particles, but also apparentlyhelp to lubricate the die surfaces or limit the frictional forces thatdevelop in press ing at high pressures.

The final strength properties attainable are dependent on the finalsintered density attained. Heretofore, aluminum parts with crushstrengths above 20,000 p.s.i. and acceptable ductility, were attainableonly by pressing to low density, sintering, and then coining to highdensities. Needless to say, elimination of coining results in greatsavings.

TABLE II Data for Aluminum4 w/ 0 copper flake single-pressed samples[#44 natural copper fine flake used in all cases] Green Sinteredsintered in dry density density Crush 0.D. dehydrogen Powder mixturepercent percent strength, flection theoret. theoret. p.s.i. percent Hrs.Temp.

Cu flake plus 92. 7 84. 8 24, 200 12. 4 0. 5 620 Reynolds 92. 7 88.9 60012. 1 0. 5 620 (#12120) free flow 92. 7 88. 5 26, 400 11. 5 0.5 620aluminum. 92. 7 86. 5 25, 900 12. 4 0. 5 620 92. 7 88. 0 26, 750 11. 1O. 5 620 92. 7 88. 4 26, 100 11. 6 0. 5 620 84. 8 83. 5 21, 400 11. 5 0.5 G 84. 8 83. 8 22, 500 11. 7 0. 5 620 Cu flake plus 85 84. 8 20, 100 9.65 0. 5 608 V.M.P. 100/200 85 84. 5 19, 700 0.16 0.5 008 mesh aluminum.75 p 75. 4 11,700 7. 23 0.5 608 75 74. 8 11, 000 7. 75 0. 5 608 Cu flakeplus 85 79.8 11, 150 12. 15 (l. 5 615 V.M.P. fine alu- 89 84. 2 12, 30010.03 0.5 615 minum needles. 95 88. 4 14, 800 9. 42 0. 5 600 rangingfrom 612 C. to 628 C. Crush strengths of 8,500 to 17,000 p.s.i. (poundsper square inch) were obtained concomitantly with O.D. deflectionsranging from 3% to 14%. Samples sintered at 614 C. to 621 C. had aslight shrinkage of .00 to .003" on the OD.

Composition B was sintered at 640 C. for /2 hour in a dry hydrogenatmosphere and densities of 96.5% of theoretical were attained.Following this the samples were coined to 100% of theoretical density;original diameter of 0.736" coined to 0.752" diameter. This was followedby resintering at 640 C. for /2 hour and the final density attained was98.5% of theoretical.

Composition C was pressed into sleeve-type cylinders in the same die asused for Com-position A. However, green density was increased to 95.5%of theoretical. The resultant compacts were then sintered at varioustemperatures and the following results obtained.

Crush Slntering Temp, C. strength, Percent O.D.

p.s.i. deflection (average) Thus, a commercially competitive method hasbeen developed for compacting aluminum powder mixtures, particularlythose containing 40 w/o and more 325 mesh aluminum. This methodinclude-s the use of a flake powder and nominal amounts of Sterotexcapable of adequately lubricating the powder to prevent galling andseizure. Furthermore, the copper flake offers a means of protecting thefine aluminum powder from contamination during the sintering process.The pressing operation can be carried out at low pressures and highpressures.

The process described herein is applicable to the production of porous,self-lubricating parts and high-density structural aluminum components.

While the flake materials has been particularly described in terms ofcopper flakes, it is understood that other flake materials can also beadded to the aluminum powder partially or completely in place of thecopper flakes, in approximately the same amount. Such other flakematerial can be, in general, any metallic element or alloy, other thanaluminum, of course, which can be produced in flake form. Representativeother metals include, for example, brass, zinc, magnesium, and tin. As atypical example, 40 mesh aluminum powders containing 40 weight percent325 mesh material is mixed with 3 weight percent brass (70% copper, 30%zinc) flake, and /2 weight percent lubricant for 30 minutes, pressed toover %of theoretical density and sintered for 30 minutes at 580 C. to620 C. in hydrogen.

While there have been shown what are considered to be preferredtechniques in accordance with the invention, it will be appreciated thatmany changes may be made therein without departing from the spiritthereof as set forth in the appended claims.

What is claimed is:

'1. A process for facilitating the compaction of particulate aluminumcomprising mixing particulate aluminum with from about 1% to 5% byweight based upon the weight of the mixture of flakes of anothermalleable metal and applying pressure to the mixture in an amountsufficient to compress the mixture to the desired density, the flakestherein acting as a sliding lubricant, thereby facilitating compaction.

2. A process as in claim 1 wherein an auxiliary die lubricant is alsopresent in the mixture before pressure application.

3. A process as in claim 1 wherein the mixture is compacted to a densityabove 80% of the theoretical density.

4. A process for facilitating the compaction of particulate aluminumcomprising mixing particulate aluminum with from about 1% to 5% basedupon the weight of the mixture of flakes of another metal selected fromthe group consisting of copper, brass, zinc, magnesium and tin andapplying pressure to the mixture in an amount suflicient to compress themixture to the desired density, the flakes therein acting as a slidinglubricant, thereby facilitating compaction.

5. A process as inclaim 4 wherein the flakes are magnesium flakes.

6. A process as in claim 4 wherein the flakes are copper flakes.

7. In the process of forming aluminum based bodies, the steps comprisingmixing aluminum powders with copper particles in flake form, the coppercontent of the mixture being between about 1% to 5% by weight, andcompacting the mixture to form a green compact, said mixture duringcompacting being subjected to pressure and said copper flake thereinacting as a sliding lubricant facilitating compaction of the mixture.

8. The process as set forth in claim 7, further including the additionof an organic die lubricant in said mixture in an amount not in excessof 5% by weight.

9. In the process of forming high-density aluminum based bodies, thesteps comprising mixing aluminum powders with copper particles in flakeform, the copper content of the mixture being between about 1% to 5% byweight, and compacting the mixture to a green density above 80% oftheoretical, said mixture during compacting being subjected to pressureand said copper flake therein acting as a sliding lubricant facilitatingcompaction of the mixture.

10. The process as set forth in claim 9, wherein the copper content isabout 2% by weight.

'11. The process as set forth in claim 9, wherein the green density isabout 95.5%.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS799,973 8/1958 Great Brita-in.

LEON D. ROSDOL, Primary Examiner.

REUBEN EPSTEIN, L. DEWAYNE RUTLEDGE,

Examiners.

. R. L. GRUDZIECKI, Assistant Examiner.

1. A PROCESS FOR FACILITATING THE COMPACTION OF PARTICULATE ALUMINUM COMPRISING MIXING PARTICULATE ALUMINUM WITH FROM ABOUT 1% TO 5% BY WEIGHT BASED UPON THE WEIGHT OF THE MIXTURE OF FLAKES OF ANOTHER MALLEABLE METAL AND APPLYING PRESSURE TO THE MIXTURE IN AN AMOUNT SUFFICIENT TO COMPRESS THE MIXTURE TO THE DESIRED DENSITY, THE FLAKES THEREIN ACTING AS A SLIDING LUBIRCANT, THEREBY FACILITATING COMPACTION. 